Fluidized sandpacking

ABSTRACT

A method for obtaining an improved pack emplacement when packing a well with sand or gravel. A slurry of sand or gravel is pumped through the end of a tubing string that is extended to near the bottom of the interval to be packed; as the slurry is pumped, the tubing string is raised at a rate that is correlated with the pumping rate in order to maintain a fluidized bed of sand around the end of the tubing string as it moves through the interval to be packed.

United States Patent Murphey, Jr. et al.

[54] FLUIDIZED SANDPACKING Tex.

[73] Assignee: Shell Oil Company, New York,

[22] Filed: Oct. 22, 1970 [21] Appl. No.: 82,925

[52] US. Cl ..l66/278 [51] Int. Cl ..F21b 43/04 [58] Field of Search..166/276, 278

[56] References Cited UNITED STATES PATENTS 2,652,117 .A qffff.if'fff'ifll 7.8

[ 1 Sept. 19, 1972 8/1954 Shea, Jr. et al. ..l66/278 5/1961 Nesbitt etal. ..l66/276 Primary Examiner-James A. Leppink Attorney-Harold L.Denkler and Theodore E. Bieber s71 ABSTRACT V A method for obtaining animproved pack emplacement when packing a well with sand or gravel. Aslurry of sand or gravel is pumped through the end of a tubing stringthat is extended to near the bottom of the interval to be packed; as theslurry is pumped, the

tubing string is raised at a rate that is correlated with the pumpingrate in order to maintain a fluidized bed of sand around the end of thetubing string as it moves through the interval to be packed.

8 Claims, 2 Drawing Figures PATENTEUSEP 19 me m f/M A TTUXPNE VBACKGROUND OF THE INVENTION l. Field of the Invention This inventionrelates to the field of completing wells. More particularly, theinvention concerns the placement of a pack of granular material in awell which penetrates an unconsolidated earthformation. I

2. Description of the Prior Art In producing petroleum from subterraneanreservoirs, many wells are drilled into or through loosely cemented orunconsolidated formations. When such a well is placed on production,sand is often carried from the formation by the fluid and deposited inthe well bore. Some sand is usually entrained in the produced fluid,thus causing severe erosion and damage to equipment whichis employedinthe production of the fluid. The production of the sand interfers withthe normal production operations and gives rise to numerousoperatingproblems. It can be generally said that in the production of afluid from a loosely consolidated formation, workovers are frequentlynecessary to remove sand from the bottom of the borehole. If the erosionof the sand aroundthe casing in the bottom of a borehole is sufficientlygreat, it will leave the casing inadequately supported and the casingmay eventually buckle or collapse. In some instances, the sand problemis so severe that the well has to be abandoned.

Various methods have been attempted or suggested to date for solving theproblem of sand production in wells that penetrate unconsolidatedformations. One of the most widely practiced methods is to place packsof granular material such as sand or gravel behind a slotted liner or aperforated casing in such wells to prevent an inflow of material fromthe surrounding incompetent earth formation. i

Such packs are installed bypumping a slurry of granular material intothe well so that the grainsuspending liquid is forced into thesurrounding earth formation while the suspended grains are screened outon the face of the earth formations. In a borehole that contains aperforated casing, the slurry must flow through the perforations thatextend laterally through the casing and through a surrounding sheath ofcement.

In accordance with conventional practice, the slurry of granular packingis pumped through a stationary tubing string positioned so that thelower end of the string is located at or above the top of the intervalto be packed. This placement of the tubing string is believed to bedesirable in order to avoid the packs being formed around a significantlength of the tubing string thus binding the tubing string within thewell.

The use of a tubing string that ends above the interval to be packedcauses the slurry to flow downward past the perforations in the casingor liner. The jetting effect of fluid emerging from the tubing stringcauses a well mixed turbulent zone of slurry within a distance of a fewcasing diameters from the end of the tubing string. However, below thisjet mixed zone, slurry moves down the casing in a relatively slow flowand forms a deposit within the well bore as lower perforations ceasetaking slurry. This well bore deposit can build up to the lower end ofthe turbulent slurry zone in the region of the tubing string. Thus, inthe conventional practice it is inevitable that arelatively largeproportion of the sand remains within the well rather than beingdisplaced into the formation.

SUMMARY OF THE INVENTION The present invention provides: an improvedmethod for packing a well with a granular packing material. According tothe invention a string of tubing is extended into the wellbore to nearthe bottom of the interval to be packed and a slurry of packing materialis then pumped through the tubing string while the string is beingraised at a rate that is correlated with the pumping rate to maintain afluidized bed of packing material around the end of the tubing string asit moves through the interval to be packed. In a preferred embodiment ofthepresent invention, when packing a well having a cemented andperforated casing the slurry is pumped at a pressure great enough tocreate a cylindricalfracture between the casing and/or cement and thewalls of the formation penetrated by the well.

DESCRIPTION OF THE PREFERRED EMBODIMENT I Referring to FIG. 1 we see anunconsolidated earth formation 10 such as an unconsolidated sandformation penetrated by a well 9 having a well bore 11 which haspenetrate the casing 12 and the surrounding cement 13. There are anumber of cavities or zones of high porosity 19-23 in the formation 10adjacent to the perforations 14-18 which zones are of a type that may becaused by sloughing or realignment of sand particles from theunconsolidated earth formation 10 as fluid flows into the well bore 11through the perforations 14-18. V

The well 9 is provided with equipment suitable for the practice of thisinvention. A string of tubing 24 extends from the surface down the wellbore 11 to near the lowermost perforation to be packed 14. At thesurface the tubing 24passes through a wellhead closure assembly 25 thatis operatively connected to the casing 12 and which is adapted to carrya wellhead seal-off means 36 of a type which may provide a fluid-tightsealoff of the annulus between the casing 12 and the tubing 24 whileallowing the tubing 24 to be raised and lowered through the wellheadassembly 25. The top of the tubing 24 is connected in fluidcommunication with a flexible conduit means such as a. hose 26 adaptedto maintain fluid communication between the tubing 24 and a conduitmeans such as a flow pipe 27 as the tubing 24 is raised and lowered. Theflow pipe 27 is in fluid communication with a slurry pumping apparatusof a conventional type (not shown).

The tubing 24 is operatively connected to a raising and lowering meansof a conventional type which may be a workover rig comprising a drawworks 28 powered by a motor means 29 and operatively connected to a wireline 30 that is strung through a crown block 31 mounted near the top ofa mast or derrick means 32 and then through a traveling block 33 that isconnected by suitable means to a; hook 134 which may be coupled to atubing elevator 35 operatively connected to the tubing string 24.

To pack zones 19-23 behind the perforated casing 12 with a granularpacking material 37 according to the process of this invention, thetubing 24 is lowered into the well bore 11 until it extends to a pointadjacent the lowermost perforation 14 in the interval to be packed.Preferably, the lower end of the tubing 24 is spotted about 12 to 24inches above the lowermost perforation 14. The annulus between tubing 24and casing 12 is preferably closed to fluid flow above the interval tobe packed as by wellhead seal-off means 36 or any other suitable means.A slurry of granular packing material 37 is then pumped through thetubing 24 into the well bore 1 1 at a rate sufficient to create a zoneof turbulent flow extending below the lowest perforation l4. Injectionrates in the range of about 1 barrel per minute to about 3 barrels perminute are normally suitable for this purpose; however, the injectionrate used in the practice of this invention may range from the minimumrate at which a slurry of a given packing material may be pumped throughthe tubing 24 without plugging to the maximum rate which can be achievedwithout fracturing the formation 10. As the slurry is pumped through thetubing 24, the tubing 24 is slowly raised through the interval to bepacked at a substantially constant rate correlated with the slurrypumping rate so that when the lower end of the tubing 24 reaches top ofthe interval to be packed all of the granular packing material intendedto be used in packing the interval has been used. This raising of thetubing 24 may be done either incrementally or substantiallycontinuously.

' Referring to FIG. 2, we see an illustration of the flow of slurry inthe well bore 11 near the end of the tubing 24. Since the annulusbetween the casing 12 and the tubing 24 is closed to fluid flow at somepoint above the interval to be packed, as by the seal-off means 36 inthe wellhead closure assembly 25 of FIG. 1, the fluid pumped down thetubing 24 into the well bore 11 can flow out the well bore only throughopenings such as perforations 14-18 in the walls of the casing 15. Asthe slurry of packing material 37 flows through the perforations 14-18into the cavities 19-23 behind the casing 15, the grain suspendingliquid component of the slurry is forced into the surrounding earthformation while the packing material 37 is screened out on the face ofthe formation 10.

As the slurry is pumpedout of the tubiiig 24, a zone 38 of turbulentflow extends across the diameter of the well bore 11 and into anyadjacent perforations, such as perforations 15 and 16 for a distance ofabout 1 to 2 feet below the end of the tubing 24. Within the turbulentzone 38 packing material 37 is churned into a fluidized bed in which thegrain density (i.e., the number of grains per unit volume) issubstantially uniform. Each perforation that is adjacent to theturbulent zone 38 tends to be penetrated by a substantially equal amountof packing material 37 as the fluidized packing material 37 flows intothe perforation. Above the turbulent zone 38, there is a zone 39 in thewell bore 11 in which the direction of flow is mainly upward. In thiszone 39, the velocity of fluid flow decreases at each perforation, suchas perforation 17,

v in proportion to the amount of slurry entering that perforation andbecomes substantially zero at about the depth of the uppermostperforation 18. Because of the decrease in slurry flow velocity in thezone 39 the flowing fluid in this zone 39 soon becomes free of suspendedpacking material 37. Thus, only a small proportion of the packingmaterial 37 is carried above the top of the turbulent zone 38. Below theturbulent zone 38, the well bore 11 becomes filled with packing material37 that has settled out of the slurry.

As the tubing string is moved upward through the interval to be packed,the zone 38 of turbulent flow is advanced up through the perforatedinterval of the casing 15 assuring that each of the cavities 14-18behind the perforated casing 15 is filled with'a substantially equalnumber of grains of the packing material 37 per unit of volume if thecharacter of the formation is uniform. The upward movement of the tubing24 and the fluidized bed of sand in the turbulent zone 38 avoids thesticking of the tubing 24 by keeping it above any sand that is not partof a fluidized bed. The process also prevents a premature filling of thewell bore 11 with packing material 37. Since the packing material 37 isintroduced at the bottom, no static deposit is allowed to form at thedepth of any of the perforations 14-l8 until after the perforation hasbeen filled with the fluidized bed of packing material.

In an embodiment of this invention, when packing an interval in acemented and perforated casing 12, the grain suspending liquid componentof the slurry of packing material 37 is forced into the surroundingearth formation 10 at an injection pressure less than fracturingpressure of the formation 10 but great enough to compress the formation10, moving the face thereof radially outward relative to the casing 12and cement l3 and creating a narrow void space or cylindrical fracturesubstantially surrounding the cement 13. The pressure at the face of theformation 10 required to create a cylindrical fracture 40 may bedetermined by injecting a quantity of the grain suspending liquid intothe formation prior to the injection of the slurry of packing material37 at a relatively low injection pressure and then increasing the bottomhole injection pressure (without exceeding the pressure at whichfractures will be created which extend laterally into the formation 10which lateral fracturing pressure may be known from other wells in thearea or may be determined by methods well known in the art) whiledetermining the injectivity of the well 9 from data obtained bymeasuring the injection pressure and the injection rate. Tests show thata marked increase in injectivity can be expected to occur at thatpressure at which a cylindrical fracture is formed.

In operating the present process, the slurry of grains to be used informing a sandpack or gravel pack can comprise a slurry of grains ofparticulate matter which are coated with a solution of epoxy resincomponents in a resin component solvent and are suspended in a liquidhydrocarbon that has a limited solubility with the resin component (asdisclosed in a copending patent application of E. H. Bruist et a1, Ser.No. 867,631, filed Oct. 20, 1969.)

While the process of this invention has been described primarily withrespect to packing an interval in a well wherein a casing has beencemented and then perforated, it should be understood that the method isequally applicable to the placement of granular packing material inwells completed in other ways, for example, as with an uncementedslotted liner or other perforated pipe member.

In summary, the present invention provides an improved method forpacking a well bore with a granular pumping a slurry of a granularpacking material through the string of tubing at a pumping ratesufficient to create a zone of turbulent flow around the end of thestring of tubing which extends across the diameter of the wellbore andin which turbulent zone the granular packing material is churned into afluidized bed in which the grain density is substantially uniform, andsimultaneously raising the string of tubing, preferably at a rate thatis correlated with the pumping rate to maintain a fluidized bed ofpacking material around the end of the string of tubing as it movesthrough the inter val to be packed. In a wellbore cased with a tubularstring of easing that is cemented in place and perforated through aninterval to be packed, an embodiment of the invention may comprise theadditional steps of determining a cylindrical fracture forming pressureless than the lateral fracturing pressure of said formation which issufficient to cause the surrounding earth formation to move outwardlyrelative to the cemented string of casing leaving a narrow space betweenthe cemented string of casing and the earth formation, and adjusting theslurry pumping rate while pumping the slurry to maintain a pressure onthe earth formation substantially equal to the cylindrical fractureforming pressure.

We claim as our invention: 1. In a wellbore cased with tubular string ofcasing that is cemented in place and perforated through an interval tobe packed to provide fluid communication with a surrounding earthformation, a method for packing the wellbore with a granular materialcomprising the steps of:

extending a string of tubing into the wellbore to a point adjacent tothe bottom of a selected interval of the wellbore to be packed, annularspace being defined between the string of tubing and the tubular casing;closing the annular space between the string of tubin g and the casingabove the interval to be packed;

determining a cylindrical fracture forming pressure less than thelateral fracturing pressure of said formation which is sufficient tocause the surrounding earth formation to move outwardly relative to thecemented string of casing leaving a narrow space between the cement andthe earth formation;

pumping a slurry of a granular packing material through the string oftubing at a slurry pumping ratesufficient to create a zone of turbulentflow around the end of the string of tubing which extends across thediameter of the wellbore and in which turbulent zone the granularpacking material is churned into a fluidized bed in which the graindensity is substantially uniform; A

adjusting said slurry pumping rate while pumping said slurry to maintaina pressure on said earth formation substantially equal to saidcylindrical fracture forming pressure; and

simultaneously raising the string of tubing through the interval to bepacked.

2. The method of claim 1 wherein the slurry of granular packing materialcomprises a slurry of grains of particulate matter which are coated witha solution of epoxy resin components and which are suspended in a liquidhydrocarbon.

3. In a wellbore penetrating a fluid containing subsurface earthformation which is cased opposite the fluid containing formation with aperforate pipe member having a plurality of perforations verticallyspaced along the length thereof, there being at least one cavityexternal of the perforate pipe member adjacent one or more of theplurality of perforations, a method for packing the interior of theperforate pipe member, the perforations in the perforate pipe member andthe cavity externalof the perforate .pipe member with a granularmaterial comprising the steps of:

extending a string of tubing into the well bore to a pointwithin theperforate pipe member adjacent the lowermost of the vertically spacedperforations;

pumping a slurry of a granular packing material through the string oftubing at a slurry pumping rate sufficient to create a zone of turbulentflow within the perforate pipe member around the end of the string oftubing in which zone of turbulent flow granular packing material ischurned into a fluidized bed in which the grain density is substantiallyuniform, said zone extending across the diameter of the perforate pipemember adjacent the lowermost perforation, through the lowermostperforation and into the cavity external of the perforate pipe memberadjacent the lowermost perforation; and, thereafter,

. raising the string of tubing through the perforate pipe member whilecontinuing to pump the slurry at the slurry pumping rate whereby thezone of turbulent flow is sequentially moved past each of the verticallyspaced perforations above the lowermost perforation, each perforation.and the interior of the perforate pipe member as well as the cavityexternal of the perforate pipe member adjacent that perforation beingfilled with granular packing material as the zone of turbulent flow ismoved past the perforation.

4. The method of claim 3 including the step of closing the well boreexternal of the string of tubing to fluid flow at a point above theperforate pipe member before pumping said slurry.

5. The method of claim 2 wherein said slurry pumping rate is a ratewithin the range of 1 barrel per minute to 3 barrels per minute.

6. The method of claim 3 wherein the step of extending a string oftubing in the well bore to a point within the perforate pipe memberadjacent the lowermost of the vertically spaced perforations compriseslowering a string of tubing into the well bore to a point at which thelowermost end of the string of tubing is less than about 2 feet abovethe lowermost perforation.

7. The method of claim 3 wherein the step of raising the string oftubing comprises raising the string of tubing through the perforate pipemember at a substantially constant rate.

8. The method of claim 7 including the steps of:

deten'nining a selected amount of granular material to be used inpacking the well bore adjacent the fluid-containing formation, and

correlating the substantially constant rate at which the tubing israised with the slurry pumping rate so that when the lower end of thetubing reaches the top of the well bore portion to be packed an amountof granular material equal to the selected amount of granular materialhas been pumped into the well bore.

1. In a wellbore cased with tubular string of casing that is cemented inplace and perforated through an interval to be packed to provide fluidcommunication with a surrounding earth formation, a method for packingthe wellbore with a granular material comprising the steps of: extendinga string of tubing into the wellbore to a point adjacent to the bottomof a selected interval of the wellbore to be packed, an annular spacebeing defined between the string of tubing and the tubular casing;closing the annular space between the string of tubing and the casingabove the interval to be packed; determining a cylindrical fractureforming pressure less than the lateral fracturing pressure of saidformation which is sufficient to cause the surrounding earth formationto move outwardly relative to the cemented string of casing leaving anarrow space between the cement and the earth formation; pumping aslurry of a granular packing material through the string of tubing at aslurry pumping rate sufficient to create a zone of turbulent flow aroundthe end of the string of tubing which extends across the diameter of thewellbore and in which turbulent zone the granular packing material ischurned into a fluidized bed in which the grain density is substantiallyuniform; adjusting said slurry pumping rate while pumping said slurry tomaintain a pressure on said earth formation substantially equal to saidcylindrical fracture forming pressure; and simultaneously raising thestring of tubing through the interval to be packed.
 2. The method ofclaim 1 wherein the slurry of granular packing material comprises aslurry of grains of particulate matter which are coated with a solutionof epoxy resin components and which are suspended in a liquidhydrocarbon.
 3. In a wellbore penetrating a fluid containing subsurfaceearth formation which is cased opposite the fluid containing formationwith a perforate pipe member having a plurality of perforationsvertically spaced along the length thereof, there being at least onecavity external of the perforate pipe member adjacent one or more of theplurality of perforations, a method for packing the interior of theperforate pipe member, the perforations in the perforate pipe member andthe cavity external of the perforate pipe member with a granularmaterial comprising the steps of: extending a string of tubing into thewell bore to a point within the perforate pipe member adjacent thelowermost of the vertically spaced perforations; pumping a slurry of agranular packing material through the string of tubing at a slurrypumping rate sufficient to create a zone of turbulent flow within theperforate pipe member around the end of the string of tubing in whichzone of turbulent flow granular packing material is churned into afluidized bed in which the grain density is substantially uniform, saidzone extending across the diameter of the perforate pipe member adjacentthe lowermost perforation, through the lowermost perforation and intothe cavity external of the perforate pipe member adjacent the lowermostperforation; and, thereafter, raising the string of tubing through theperforate pipe member while continuing to pump the slurry at the slurrypumping rate whereby the zone of turbulent flow is sequentially movedpast each of the vertically spaced perforations above the lowermostperforation, each perforation and the interior of the perforate pipemember as well as the cavity external of the perforate pipe memberadjacent that perforation being filled with granular packing material asthe zone of turbulent flow is moved past the perforation.
 4. The methodof claim 3 including the step of closing the well bore external of thestring of tubing to fluid flow at a point above the perforate pipemember before pumping said slurry.
 5. The method of claim 2 wherein saidslurry pumping rate is a rate within the range of 1 barrel per minute to3 barrels per minute.
 6. The method of claim 3 wherein the step ofextending a string of tubing in the well bore to a point within theperforate pipe member adjacent the lowermost of the vertically spacedperforations comprises lowering a string of tubing into the well bore toa point at which the lowermost end of the string of tubing is less thanabout 2 feet above the lowermost perforation.
 7. The method of claim 3wherein the step of raising the string of tubing comprises raising thestring of tubing through the perforate pipe member at a substantiallyconstant rate.
 8. The method of claim 7 including the steps of:determining a selected amount of granular material to be used in packingthe well bore adjacent the fluid-containing formation, and correlatingthe substantially constant rate at which the tubing is raised with theslurry pumping rate so that when the lower end of the tubing reaches thetop of the well bore portion to be packed an amount of granular materialequal to the selected amount of granular material has been pumped intothe well bore.